To generate light to illuminate an object that is to be observed by an endoscope, tungsten halogen lamps and especially gas discharge lamps are primarily used, for example xenon-short arc lamps, other halide short arc lamps and high-pressure mercury vapor lamps. These light sources are customarily combined in a light source device with their own power source, a control or regulation filter and a blower for discharging waste heat. The light source device is produced as a separate unit from its own endoscope and is connected with the proximal end of the endoscope by a light conductor cable.
Disadvantages of the aforementioned light sources concern the degree of effectiveness or power requirement and waste heat, dimension and modular capacity. An attractive alternative concerning these aspects consists in light diodes, in particular inorganic semiconductor light diodes, and increasingly also organic light diodes. A disadvantage of a light diode, in comparison to a conventional light source, consists in the fact that not only the radiant flux Phi generated by it, but also the specific irradiance R (in Wm−2) and the emittance B=d2Phi/dA d Omicron cos(0) (in Wm−2 steradians−1) are smaller or definitely smaller than with conventional light sources. The radiant power also that can be coupled into the light conductor cable to transmit the illuminating light to the endoscope has therefore been smaller heretofore.
Light from a conventional light source, because of the high achievable radiant capacity and intensity, can be filtered to generate, for instance, excitation light for autofluorescence or for fluorescence of protoporphyrin IX induced by 5-aminolevulinic acid (ALA) previously administered to a patient or for fluorescence of indocyanine green. The excitation filter being used is as a rule transparent only in a narrow wavelength range, in order to avoid over-radiation of the weak fluorescent light by remitted excitation light.
If a conventional light source is replaced by a white light diode, there remains after a corresponding filtering only a low radiant capacity in the desired narrow range of the excitation light, because of the aforementioned disadvantages of the light diode. This low radiant capacity typically no longer suffices to achieve sufficient illumination in the desired object distances or to sufficiently illuminate large hollow spaces. What is desired is therefore a light source device in which a spectrum generated by the light source device is feasible not subtractively by removing a filter, but additively by mixing or combining light from several light sources.